Conventional ink jet printers make use of square or rectangular shaped heater resistors. The primary advantage of square or rectangular shaped thin film resistors is their electrical simplicity. In a square or rectangular shaped resistor, the direct current (DC) resistance is directly proportional to the length/width ratio (L/W), often referred to as the number of squares. By knowing the sheet resistance of the thin film and the L/W ratio, the DC resistance value of the thin film resistor can be calculated.
Unlike in a typical electronic application where a thin film resistor is a passive element in the circuit, the thin film resistor used as an ink ejector in an ink jet printer is an active element. The thermodynamics and hydrodynamics of the ink in conjunction with the thin film resistor make design of these devices much more complicated than if the thin film resistor were a passive element in the circuit. Accordingly, use of square or rectangular shaped resistors, while simplifying the construction, do not lead to the most energy efficient heater resistors. Furthermore, many resistor shapes, including square or rectangular shapes can contribute to ejector misfires due to air build up in ink chambers adjacent the resistors.
There continues to be a need for more energy efficient ink ejectors so that a higher density of ink ejectors can be placed on a printhead chip without excessively heating the chip. There is also a need for heater resistor designs which reduce misfiring caused by air build up in the ink chambers adjacent the chips.